1. Field of the Invention
The present invention relates generally to sensing of physical phenomena in an environment, particularly to sensing RF sources in an environment, and more particularly to utilizing digital beamforming techniques to detect RF sources in an environment and visually providing spatial awareness of the location of the RF source.
2. Description of the Related Art
Military soldiers are called upon to execute a wide variety of missions. Some of the most dangerous missions involve engagement of enemy forces that place soldiers in harm's way. Providing superior information to soldiers is an important means of establishing a tactical advantage that can greatly increase the probability of survival of the soldier and successful execution of important missions. Enemy forces commonly utilize communication equipment ranging from consumer cell phones to sophisticated military radio transceivers. The ability to visually survey an environment to identify, locate and characterize RF sources can be beneficial in a variety of applications. For example, visually mapping the RF sources in an environment might reveal the presence and location of enemy forces that would otherwise remain concealed and potentially lethal.
Characterizing the RF environment at some location and time can be challenging. There may be many transmit sources of different frequencies and bandwidths received with different power levels. A spectrum analyzer can identify the presence of RF energy in a given band, but does not generally identify the location from which the energy arrived. A directional antenna used with a spectrum analyzer could help isolate an RF source, but may have other limitations, such as a fixed beamwidth, mechanical steering, and an inability to analyze multiple directions simultaneously.
U.S. Pat. No. 5,307,077, entitled “Multi-Spectral Seeker Antenna” issued to John T. Branigan et al, discloses a multi-spectral seeker system for detecting radiation in the infrared (IR) band and a plurality of radio frequency (RF) bands suitable for use in a guided missile is disclosed. The IR and RF seekers are coaxially integrated on a single gimbaled platform and share a common aperture without significant performance degradation. In the preferred embodiment, the IR seeker uses a Cassegrainian reflector assembly with surfaces reflective to IR but transparent to RF signals. The first RF seeker uses a resonant dichroic reflector antenna which is transparent to RF signals at frequencies no closer than 0.5 octaves from the dichroic reflector system operating frequency. The second RF seeker may use any suitable RF antenna system although a planar-array of multi-mode spiral antennas or a standard flat plate slotted array are preferred. The second RF seeker may operate in an active, semi-active, or passive mode. The IR seeker means and both RF seeker means together provide coaxial seeking in a single aperture covering three frequency bands without significant loss of performance in the RF antenna and IR sensor. The material on which the parabolic reflector is formed is tapered in thickness as a function of radius to eliminate phase delays introduced by the curvature as seen by the second RF seeker.
Branigan et al requires a high performance mechanically steered antenna structure, which is challenging to implement and may be physically large. As will be disclosed below, the present invention overcomes these limitations with electronic steering by way of digital beam forming.